The mechanism whereby the catecholamine content of carotid bodies is regulated by physiologic or pharmacologic stimuli was studied. Hypoxia and stimulation of muscarinic receptors increases the rate of dopamine release without changing its turnover-rate. Neither the carotid sinus nor the sympathetic nerves participate in the modification of dopamine content by both types of stimuli. In contrast, carbohydrate-active steroids cause a short-term increase of dopamine content which appears to be due to blockade of dopamine metabolism.